Reduction of nitro compounds



I 1,644,483 1927' R. A. NELSON ET AL REDUCTION OF NITRO COMPOUNDS FiledJune 22, 1920 Patented C at. 4, 1927.

U f' TE RALPH A. NELSON AND ANTON PRASIL, F BUFFALO, NEW YORK, ASSIGNORSTO NATIONAL ANILINE & CHEMICAL COMPANY, INC., OF NEW YORK, N. Y., A COR-POBATION OF NEW YORK.

nnnnc'rron on nrrno oorrr'ounns.

Application filed June 22, 1920. Serial No. 390,884,

This invention relates to improvements in the reduction of nitrocompounds, and more particularly tothe reduction of nitro compounds tohydrazo compounds, by means of zinc and caustic alkali as the reducing.agents. The invention also relates to 1mprovements in the separation andisolation of the hydrazo compounds, at the end of the reduction, wherebythe hydrazo compounds are obtained in an isolated state. The inventionincludes improvements in the reduction operation, in the extraction andisolation operation, and in the combined reduction and isolationoperations.

In the reduction of nitro compounds to hydrazo compounds, it hasheretofore been proposed to effect the reduction by means of zinc andcaustic, all of the zinc being added' first and the alkali beinggradually added, or all of the caustic alkali being added first and thezinc being gradually added. In

proceeding this way it is difficult to confine the reduction to thehydrazo stage and obtain good yields, the tendency being either for thereaction to proceed incompletely, or

to'proceed too energetically with the resulting reduction of the nitrocompound to amido compounds.

In the separation of the hydrazo compound, at the end of the reduction,when alcohol has been used as the solvent, it has been proposed toseparate the'zinc residue from the hydrazo compound by extraction withacid. When acid is used,'the caustic present in admixture with thehydrazo compound is neutralized so that it cannot be recovered and sothat a corresponding amount of acid is used up in its'neutralization,while the zinc is similarly dissolved and converted into a-salt andrequires a corresponding amount of acid for its solution. The use ofacid in this way also tends to zonvert the hydrazo compound, byrearrangement, into a compound of the benzidine series, which is solublein the acid solution.

According to the present invention objections of the character abovereferred to are largely overcome or minimized and the reduction andseparation operations are carried out man improved and advantageousmanner, with the production of hydrazo compounds with high yields.

According to the present invention, the nitro compound, in alcoholsolution, is subcases, be separated mechanically, but such .esses inwhich the alcohol is removed b jected to reduction by means of zinc andcaustic alkali, but instead of adding all of the caustic or all ofthealkali at the outset and attempting. to regulate the reduction by thegradual addition of the other reagent, the zinc and caustic areintermittently added so that the reaction can be more readily andadvantageously controlled. The intermittent addition ofthe reagents, inaddition to affording better control of the reduction, avoids theaccumulation of the reagents with the possibility of their sudden lytaking hold and causing the reaction tov proceed with explosiveviolence.

The gradual and intermittent addition of the zinc and caustic makespossible the regulation of thercduction in such away that the reductionmay be stopped at the azoxy or azo stage, while it also makes possiblethe continuation of the reduction to the hydrazo stage, with substantialcompletion, and with but a relatively small amount of overreduction tothe amido compounds.

At the end of the reduction, the crystals of the hydrazo compound, can,in certain mechanical separation involves a mechanical loss, and leavesa certainamount of zinc with the crystals, which zinc produces a loss inthe subsequent rearrangement process, if the crystals are used in thatprocess. It is 111016'85 advantageous, at the end ofthe reduction, torecover the alcohol by direct distillation, in a highly concentratedstate so it can be used directly in a subsequent reduction. The hydrazocompound is then separated from the zinc residue by extraction with anorganic solvent immiscible with water, such as benzol, for example. Inthe distillation of thealcohol, the use of steam or of water is avoided,so that the zinc reduction residue is left in a form particularly welladapted for extraction by means of the solvent, and the hydrazo compoundcan thus be extracted with substantial completion and obtained in anisolated state of high purity while the zinc oxide residue is likewiseleft me state adapting it for use for special p-urposes without furthertreatment. The present process is thus distinguished from proc- I05steam distillation, with resulting dilution of the alcohol whichprevents its further use without concentration, and also from prior inan isolated state.

proposals to distill the alcohol after dilu-.

tion of the reduction product with water, in which case the alcohol islikewise obtained in a dilute state, and the zinc residue and admixedhydrazo compound are obtained in a form preventing or making difficultthe satisfactory extraction of the hydrazo compound.

It will t hus be seen that the process of the present invention, in .itsentirety, involves the-reduction of the nitro compound in the presenceof.alcohol by the intermittent addition of zinc and caustic alkali, thesubsequent direct distillation and recovery of the alcohol, and theextraction of the hydrazocompound from the resulting reduction mass bymeans of an immiscible solvent so that the hydrazo compound is obtainedin a state of purity and with excellent yields, while the zinc residueis likewise obtained It will also be seen that the various steps of theprocess, aswell as the process in lts' entirety, present features Io-nitranisol and 15 gallons of denatured.

of novelty and of advantage.

The invention will be further illustrated by the following specificexamples:

Reduction of 0.-nitraxnisoZ.-15O pounds of alcohol (denatured, forexample, with wood alcohol and pyridin or with benzol) are .mixedtogether in a steam jacketed iron-kettle, provided with a refluxcondenser, and brou ht to a boil. .The mixture is maintaine in vigorousagitation and the reduction is effected by the intermittent andprogressive addition of zinc dust and caustic soda, adding one or theother as needed at such a rate as to keep up a vigorous reflux action,the total amount of caustic being about 16 pounds of to B. and thetotalamount of zinc dust being about 190 pounds of dust the amount ofcaustic soda corresponding to about 52-25% of the theoretical amount ofcaustic alkalinecessary. to transfer the zinc to alkali metal zincate.In the operation of the process, a part of the zinc may be firs-t added,for example, an' amount of 10 to 15 pounds thoroughly admixed with thecharge, and

then about 3- pounds of caustic soda added to bring about a vigorousreaction; A further small amount of zinc and of caustic may be add'edifthe reaction does not proceedat once. Once the reaction has started, itcan be kept up for some time by the addition-offu'rther amounts ofzincalone, further amounts of caustic-being added when required toinsure, active continuation of the reaction. The intermittent additionof the zinc and caustic in this Way prevents the ac qcumulation of anylarge excess of reagents and resulting explosion should they take holdsuddenly; and 'cau'sejfthe reaction to proceed with explosive violence.The entire period of .timerequired for the completion of the reduction;may amount to several hours, the reduction mass being heated until thereaction is complete. The

operation may thus be carried out, for'ex-' ample, over a period of from.6 to 1O hours,

' by adding about pounds of zinc dust progressively during the first 1to 2 hours,

a further portion of 40 pounds during the next two hours, and the lastportion of 40 Y above noted, the reaction may be continued for aconsiderable time by further additions of zinc without further additionsof caustic, and with addltions of caustic only when. the

. further addition of zinc fails to' give a vigorous reaction. Thecaustic soda acts as an accelerator, particularly in continuing thereaction from the azoxy to the azo stage, after which further additionsof caustic have :relatively little effect. The reduction can befollowed, to and through-the azoxy and azo stages, and then to thehydrazo stage. During the last stage of the reduction the remaining zincis added more slowly and-the reflux iscontinued by means of steam heatin the jacket of the kettle, the reduction as a whole appearing toprogress more slowly during this stage. It is of advantage, when thehydrazo crystals begin to separate out on testing, to hasten thecompletion of the reduction by adding about 15 pounds of zinc dust insmall portions at short intervals.

The progress of the reaction on reduction 'can be followed by takingsamples of the reduction mass ,and spotting them on paper. 'As thereduction nears completion the crystals separating become larger and aremore yellow in color and crystallize out rapidly. The crystals remainyellow until the reduction is complete when they suddenly become almostcolorless. Upon completion of the reduction to the hydrazo stage, themass may tend to foam somewhat, in which case the foaming may be checkedby cooling of the reaction'kettle. The avoidance' of any large excess ofzinc dust also tends to prevent excessivefoaming.

After complete reduction, the mixture is of a light gray 'color, andrelatively thick,

so that the zinc oxide does not readily 'separate from, the solution.The alcohol is then distilled off by dlrect heating (e. g. with tliesteam jacket), and directly recovered in a highly concentrated. stateso. that {itis directly available for reuse. The greater part of thealcohol ean'be recovered in this way.

The process has the advantage that a relatively small amount of alcoholis required,

"and that the alcohol can be directly recovered, without appreciabledilution, for reuse.

Furthermore, the direct distillation of the alcohol in this way leavesthe residue in a That is, the reduced mass, after distillation of thealcohol, is somewhat thick and granular as distinguished from a sludge.This mass is of a steel gray color.

Ewtractz'on of hydrazamisolr-After the removal of the alcohol bydistillation, the residue, consisting mainly of the hydrazanisol withsome small amounts of anisidine, and of the zinc oxide residue-admixedwith some caustic soda or sodium zincate, is cooled to about C., andabout 40 gallons of benzene added, and the mixture agitated until astrong solution of the hydrazanisol 'in benzene is obtained, forexample, for a period of about 1 hour. The mixture is then transferredto a settling tank, the zinc permitted to settle, and the benzenesolution decanted. The zinc residue is further extracted by the additionof further amounts of benzene until all of the h drazanisol has beenextracted, leaving the zinc residue in a relatively pure state. Thetotal amount of benzene used may amount to 80 gallons or more. It willbe evident that the particular mode of effecting the extraction of thehydrazanisol from the zinc residue is capable of considerable variation.The benzene used for the subsequent extraction or washing of theresidue, and containing relatively less hydrazanisol, can with advantagebe used in extracting hydrazanisol from subsequent reduction products.After the completionof the 'extraction, the remaining benzene held bythe zinc residue canbe' recovered by distillation. The zinc oxideresidue is substantially free from organic matter and of suflicientpurity so that it can be directly disposed of, without previousincineration,

, for special purposes. Similarly the hydrazo compound, althoughproduced by the action of zinc, is nevertheless free from zinc. That is,the process of the present invention enables a substantially completerecovery of both the zinc residue and of the hydrazo compounds to beobtained. Q L

The hydrazo compound is moreover obtained in solution in thenon-iniscibie solvent, from which it can be separated bycrystallization, or by distilling ofi' the solvent, either directly, orby means of steam or an inert gas. By crystallization from the solvent,or by distillation of the solvent, the hydrazo compound can obtained inan isolated state well adapted for further treatment or use. Thesolution of the hydrazo compound is also available for use directly forthe conversion ofthe hydrazanisol, by rearrangement with acid, todianisidine; and solutions of other hydrazo compounds can similarly beproduced and treated for the conversion of the hydrazo compound to thecorresponding 'compound of the bensidine series, for example, as setforth in application Serial No. 390886, filed J une' 22, 1920.

Instead of using benzene for the extraction of the hydrazo compound fromthe Zinc residue, other non-miscible solvents, such as toluene, may besimilarly used. I

So also, instead of reducing o-nitranisol to hydrazanisol, other nitrocompounds can be reduced to the corresponding hydrazo compounds in. asimilar manner; for example, nitro-benzene can be similarly reduced tohydrazo-benzene and o-nitro-toluene can be similarly reduced totolidine, the reduction in each case passing from the nitro, through theazoxy and azo stages, to the hydrazo stage.

A suitable apparatus for the practice of the invention isillustrated, ina somewhat conventional and diagrammatic manner, in the accompanyingdrawings. The appara .tus illustrated comprises a jacketed cast ironkettle 1 having a cover 2 and heating or cooling jacket 3 and havinga'relatively large upwardly extending reflux pipe 4 leading to thecondenser 5 from which the return pipe 6 returns the condensate eitherto the kettle or through thebranch pipe 9 to a storage tank. The returnpipe 6 has lass sights 7 and 8 therein by means of which the flow of thecondensate can be observed.

i The kettle is provided with feeding means for feeding the powderedzinc which includes the hopper 10 and the connecting pipe 11 having twoquick acting valves 12 and l3 therein. The return pipe 6 from thecondenser enters the pipe 11' between thevvalves 12 and 13, thearrangement being such that the valve 12 can be opened to ermit thepowdered zinc to enter from the opper 10, and the valve 12' can then beclosed and the valve 13 opened to permit the zinc to enter the kettle.The returning condensate assists in washing the zinc ,down into thekettle. Storage tanks 14, 15 and 16 are provlded for the alcohol, forthe benzene or other immiscible solvent, and for the ortho-nitranisol orother nitrocompound. These storage tanks .connect with the reductionkettle through the pipe 17 and the reflux pipe 4. A storage tank for thecaustic alkali is indicated at 18 connecting with the kettlethrough thepipe 19 and reflux pipe 4.

The heating and cooling jacket is provided with suitable steam and waterconnections,

the steam inlet pipe being indicated at 20,

an outlet pipe at 21, the water supply pipe at 22 and drain pipe at 26.Branch pipes for water are indicated at 23 and 24, the pipe 24permitting water to flow upon the outside of the kettle, stythat thiscontents of the kettle.

can be blown out by the application of air pressure above the liquidcontents thereof,

a 'air presure'being introduced through pipe 29. The reflux pipe 4 isprovided with a glass sight 28 for observing the flow of liquid andvapor therethrough. The pressure indicator 30 is also proyided, and thecover has a suitable manhole, not shown, for gainaccess to the interiorof the kettle.

in Tn the operation of the aparatu's, for example, the nitro compoundand-the .alcohol are introduced from the respective storage tanks intothe kettle, and heated, with agitation, to a refluxing temperature, apart of. the zinc dustthen added from the hopper 10 by closing the lower'valve 13, opening up er valve 12, permitting the zinc to pour in tweenthe valves, then closing the upper valve and opening the lower one, sothat the zinc drops into the kettle and is washed down by the refluxingalcohol. After thorough agitation and continued refluxing the causticsodais added with resulting vigorous reaction. The rate. of reaction canbe followed by means of the sight glasses in the vapor line 4 and in thereturn pipe 6.

.Near the completion of the reduction, the mass tends to foam somewhat.When foaming is indicated in the sight glass in the vapor line, watercan be run on to the surface of the kettle and into the 1acketto coolthe reacting mass and check the foaming. The avoidance of anyconsiderable excess of zinc likewise tends to decrease the foamingtendency.

a Any pressure developed during the operation of the apparatus is takencare 'of by the pipe 9 which acts as a vent. A too vigorous] reactioncan be checked by running cooling water on to the -surface of the kettleand through the jacket. When the reduction is complete, the alcohol canbe distilled off throu h the condenser and the branch pipe 9 an ,therebyrecovered in a concentrated p 'poundsby reduction of nitro compounds by7 state available for reuse. After cooling the residue, the benzene orother immisc ble solvent is added and thoroughly agitated and then blowninto, settling tanks (not shown) through the blow-out pipe 27 by meansof air pressure applied above the contents of the kettle, or dischargedby gravity through the outlet- 27.

of alcohol, directly distilling oil the alcohol at the end'of thereduction, and extracting the hydrazo compound from the zinc residue bya solvent immiscible with water.

distilling oil the alcohol, and extracting the hydrazo compound from thezinc residue by means of an organic solvent immiscible with water.

3. The method of reducing nitro compounds to hydrazocompounds and ofseparating the resulting hyrazo compounds, which comprises su'bJectingthe nitro compounds to reduction with zinc and caustic alkali in thepresence of alcohol, the reduction being carried out with the use of asmall amount of caustic alkali, and with intermittent addition of thezinc and alkali, dis.- tilling off the alcohol from the reduction massand thereby obtaining the reduction mass ina 'form well adap-ted forextraction, and extracting the hydra-Z0 compound from thezinc residue bymeans of an organic solvent immiscible with water. i

4. The method of producing and isolating hydrazanisol, which comprisessubjecting o-nitranisol to reductionwith zinc and caustic alkali in thepresence of alcohol, d is 5. The method of separating hydrazani'sol fromadmixture with zinc oxide residues and alcohol, whichcomprisesdistilling off the alcohol, and extracting the hydrazanisolfrom the. zinc residue with a low boiling solvent of the benzene series.

6. ln the production of hydrazo comounds by reduction of nitro compoundsy means of zinc and caustic alkali in the presence of. alcohol, thesteps comprising the removal of the alcohol by distillation andextracting the hydrazo coin-pounds from the residues by means of aliquid hydrocarbon solvent. i

7. In the. production of hydrazo com-.

means of zinc and caustic alkali in the presence of alcohol, the stepscomprising the removal and recovery of the alcohol by directdistillation and extracting the hydrazo compounds from the res'dues bymeansof an aromatic hydrocarbon solvent.

8. In the production of hydraz'o com- .pounds by reduction of nitrocompounds by meansot' zinc and caustic alkali in the presence ofalcohol, the steps comprising the re moval of the alcohol bydistillation and extracting the hydrazo compounds from the residue withbenzene.

9. The method of separating hydrazanisol from admixture with alkalinezinc residues and alcohol, which comprises the removal of I the alcoholby the hydrazanlsol from the residue with benzene.

10. The method of producing and isolating hydrazo compounds, whichcomprises subjecting a nitro compound, in the presence of alcohol, toreduction with zinc and about 2 to 2.6% of the amount of caustic alkalinecessary to transform the zinc into alkali zincate, directly distillingofi' the alcohol at the end of the reduction and extracting thehydrazocompounds from the zinc residue by a solvent immiscible withwater.

11. The method of producing and isolating hydrazo compounds, whichcomprises subjecting a nitro compound, in the presence of alcohol, toreduction With zinc and about 2 to 2.6% of the amount of caustic alkalinecessary to transform the zinc into alkali zincate, directly distillingoil the alcohol at the end of the reduction, and extracting the hydrazocompounds from thezinc residue by an aromatic hydrocarbon solvent.

12. The method of producing and isolatdistillation and extracting inghydrazanisol, which comprises subjecting nitranisol, in the presence ofalcohol, to reduction with zinc and about 2 to 2.6% of the amount ofcaustic alkali necessary totransform the zinc into alkali zincate,directly distilling oil the alcohol at the end of the reduction andextracting the hydrazanis01 from the zinc residue by a solventimmiscible with water.

13. The method of producing and isolating hydrazanisol, which comprisessub'ecting nitranisol, in the presence of alcoho to reduction with zincand about 2 to 2.6% of y the amount of caustic alkali necessary totransform the zinc into alkali zincate, directly distilling oil thealcohol at the end of the reduction and extracting the hydrazanisol fromthe zinc residue by an aromatic hydrocarbon solvent.

In testimony whereof we aflix our signatures.

RALPH A. NELSON. ANTON PRASIL.

